The invention pertains to drilling and rock excavation including drilling for exploration, mining, mineral development, and sampling and monitoring wells such as gas, oil and water wells. The invention will be applicable to the mining industry, the dimension stone industry, the construction industry, the oil and gas industry, and any other industries that are involved in the drilling, cutting, and grinding of rock, coal, or concrete, or in tunneling through rock. Furthermore, the invention should be applicable to the cutting, drilling, and grinding of other materials including metals, ceramics, other refractory materials, and also biological caries as in dental drilling of teeth.
Drilling and rock excavation represent a significant segment of the total mining system, and yearly drilling costs for five segments of the mining industry, namely copper/molybdenum, iron/titanium, lead/zinc, gold/silver, and crushed/dimension stone in the United States are about 1.5 billion dollars. Drill bit costs represent about 600 million dollars per year or about 40 percent of the total drilling costs. Increasing the bit life by 100 percent can translate into yearly savings of 300 million in drill bit costs.
Significant savings could also be achieved if a method is devised for greatly enhancing the penetration rate and the total penetration associated with rock drilling and tunneling while simultaneously extending the life of the bits, cutting tools and grinding media. Therefore, significant savings could be realized in general drilling costs if a method is devised which allows for increased drilling rates at constant applied mechanical stress during the drilling or tunneling, yet which at the same time prevents bit wear.
Known in the prior art are methods of maintaining the properties and parameters of a drilling fluid by introducing chemical agents into the drilling fluid while it circulates in a well. For example, Mamadzhanov et al in U.S. Pat. No. 4,410,052, issued Oct. 18, 1983, maintain the well integrity by adjusting the redox potential of the flushing fluid to the value determined at the moment of tapping the bed rock. This eliminates the ion exchange reactions between the bed walls and the flushing fluid and therefore maintains the natural permeability of the oil or gas productive well. This method is not concerned with enhancing drilling for excavation. Mamadzhanov et al in U.S. Pat. No. 4,385,666, issued May 31, 1983, maintain and control the properties and parameters of drilling muds by adjusting their oxidation/reduction potential (redox) at present values. This is done to maintain the rheological stability of the drilling mud which often gets diluted and changed in composition by ion exchange reactions in deep oil and gas well drilling and not to enhance the drilling rate or prolonging the drill bit life. Alekhin et al in U.S. Pat. No. 4,342,222, issued Aug. 3, 1982, used the redox potential of the drilling mud to determine the depth of a fluid-saturated stratum and the type of fluid such as mineralized water, oil, or gas released. Mixing the drilling mud with any of these fluid types changes its redox potential in a given direction, which identifies the nature of the fluid. This does not effect enhanced drilling productivity. Johnson and Kelly in U.S. Pat. No. 3,307,625, issued Mar. 7, 1967, pertains to wells formed when a subsurface source of hydrogen sulfide (H.sub.2 S) is encountered. Liberation of H.sub.2 S (a weak acid) can lower the pH of water to a point where the drill metal starts to corrode. To prevent this corrosion, they added an alkali metal hydroxide or sulfide, e.g. NaOH or Na.sub.2 S to raise the pH of the drilling fluid to the 7 to 9 range. None of these prior art references mentioned above are pertinent to increasing drilling productivity.
It has been found that maximum increases in drill penetration can be obtained simultaneously with maximum increases in bit life by using concentrations of chemical additive solutions, such as cationic organic surfactant and inorganic salt solutions, that neutralize the naturally-occurring negative charge on the rock surface, thereby producing a zero zeta potential or zero surface charge (ZSC) condition (cf., Engelmann et al, Zeta Potential Control for Simultaneous Enhancement of Penetration Rates and Bit Life in Rock Drilling, BuMines RI 9103, (1987), and Zeta Potential Control for Enhanced Drilling of Taconite and Other Hard Rocks, 60th Annual Meeting of the Minnesota Section, AIME and 48th Annual Mining symposium, pp. 6-1 to 6-22; and Khalafalla et al, U.S. Pat. No. 4,765,445).
The present invention provides a means for enhancing drilling rates while also prolonging the bit life at constant applied mechanical stress during drilling operations. This is accomplished by virtue of the discovery that enhanced drilling rates are a function of the rock surface condition, and that, if the rock surface is maintained at the zero point of charge (ZPC), or zero surface charge (ZSC) condition, regardless of the salt type or concentration or water source, enhanced drilling rates coupled with prolongation of the bit life are obtained. It has now been determined that water-soluble, nonionic, high molecular weight, organic polymers such as the polyalkylene oxide class of polymers including polyethylene oxide (PEO) are able to produce the ZSC condition.